Honing worn out small dovetails

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Honing worn out small dovetails

Home Forums Hints And Tips for model engineers Honing worn out small dovetails

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  • #93106
    Steve Wan
    Participant
      @stevewan33894

      Hi workshop buddies,

      I like to share with you guys a small discovery! Hand scraping may be good for dovetails of medium to large machines but I'm refering to small dovetails in the range of Sherline, Taig or Cowells machines. The new Taig comes with detachable dovetails which are good with this method.

      I re-designed the honing guide (wood-working blade sharpener with adjustable back angle) to hold the dovetail blade. With the aid of the female dovetail part plus a back lighting, I match both dovetails to spot the high/low spot with this in mind, I could adjust the honing guide to the exact angle. Simply, sand down on a sandpaper resting on a flat slab. To spot the high and low along the dovetails, use some blue and run along the surface, rub against the mating part. Sand down the high spot by applying different pressure on the honing guide. The honing guide is able to maintain a parallel flatness without the usual free hand guessing!

      Steve Wan

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      #30386
      Steve Wan
      Participant
        @stevewan33894
        #93107
        Sam Stones
        Participant
          @samstones42903

          Hi Steve,

          My Taig Micromill had certain sliding parts made from extruded aluminium including the table, which were subsequently anodised.

          I can't remember which other parts were treated this way, but wouldn't honing remove some or all of the aluminium oxide?

          Alternatively, wouldn't the anodised surface be too hard for most honing materials?

          Best regards,

          Sam

           

          Edited By Sam Stones on 26/06/2012 06:33:29

          #93110
          Steve Wan
          Participant
            @stevewan33894

            Hi Sam

            Anodised aluminium surface is only for better finish and appearance. The surface is not hard at all. With fine grade sandpaper does the job easily. For dovetails that are heat treated or case hardening, an oil stone would be a better option for honing/lapping.

            Most parts of my Sherline are made of aluminium but Taig has more steel.

            Honing is prefered than hand scraping for small parts.

            Steve Wan

            #93117
            Ian S C
            Participant
              @iansc

              Just try to keep the dove tails parallel. A bit of rod each side and measure over this at each end of the slide way. Ian S C

              #93119
              KWIL
              Participant
                @kwil

                I have never understood why anyone would want to use aluminium (or an alloy thereof ) for a dovetail slide, far too soft to have any life at all, unless it is a specialised aircraft grade which somehow I doubt.

                #93120
                David Littlewood
                Participant
                  @davidlittlewood51847

                  Steve,

                  Anodising does not increase hardness? B******t, it can increase it by a factor of 4 or more, depending on how it is done. See for example **LINK**

                  I do agree with KWIL, Al is not something I would normally consider for a sliding surface; ecven after anodising it can be too prone to galling.

                  David

                  #93130
                  Jeff Dayman
                  Participant
                    @jeffdayman43397

                    The ONLY reason aluminum extrusion is used in Sherline and other small USA made machines is that it is much cheaper than steel or iron parts to manufacture.

                    These machines are OK as long as they are not overloaded and cuts are kept light.

                    I know a couple of people with Sherline machines, one mill one lathe, and they do not report excessive wear, but they have left the wear surfaces alone (no scraping) and have used recommended lubrication.

                    If you scrape off the anodized layer (likely only 1 or 2 thou thick) the wear may increase rapidly.

                    JD

                    #93143
                    Bazyle
                    Participant
                      @bazyle

                      Perhaps they could be improved with ptfe sheet ?

                      Ali slides of various forms (extrusions) are popular with 3D printing and various lightweight CNC machines.

                      #93159
                      Sam Stones
                      Participant
                        @samstones42903

                        Hi Steve,

                        With respect, I was almost as surprised to read your comments about aluminium oxide, as I was when I received delivery of my Taig Micromill.

                        When I ordered the mill, I had done very little research, having been blinded by the thoughts of extending my CAD facilities with CAM. I sold the mill several years ago when I also disposed of my other workshop machinery. Therefore, I’m not really in a good position to comment about the mill’s sliding surfaces.

                        However, having come up through a six-year toolmaking apprenticeship commencing in 1950, and an ongoing contact with machine tools since then, it took a relatively new way of thinking when using the mill with its major components made from extruded and anodised aluminium. Upon reflection, I suppose that the forces required to accelerate the table in the X and Y directions would be less. Arguably beneficial in terms of small stepper motors which could lose their place through slippage.

                        As for aluminium oxide, in those early days when I entered the fray, it was common practice with company-issued pint pots, to initial their ownership by scratching through the glazed pottery with a piece of aluminium. This practice would also leave a black(ish), relatively indelible, deposit.

                        Also of significance was the fact that the vast majority of grinding wheels were aluminium oxide. (I can’t recall seeing more than one or two diamond grinding wheels.)

                        May I suggest a quick look at Mohs' Hardness scale which indicates that diamond gives a reading of 10, while aluminium oxide is close behind with a reading of 9.

                        In terms of lapping, honing, or scraping – once the (anodised) oxide layer has been removed, I would consider that a sliding surface would be well and truly stuffed. Try rubbing two bits of (clean) aluminium together and see what happens. It's quite gallingwink 2

                        Best regards,

                        Sam

                        Edited By Sam Stones on 26/06/2012 23:46:45

                        #93162
                        Steve Wan
                        Participant
                          @stevewan33894

                          Hi Ian SC, Sam, Kwil and all,

                          Thanks for the fruitful replies! Yes I agree that aluminium may gall or bind with each other which I encountered. Normally for light small sliding surfaces is ok with aluminium with proper lubricant. As for bigger counterparts, I would use a steel dovetail mates with aluminium reason being I want to replace the softer metal only when wear and not both. Moreover, with my small horizontal mill in the making, I would also use a steel plate to prevent aluminium blocks from galling each other. Steel does not gall with aluminium.

                          I was a toolmaker in the 80s, then hardly I saw tools made in aluminium usually cast iron. Owing to cheaper manufacturing ways and cost cutting measures aluminium is used instead. Plastic is replacing aluminium soon!

                          Steve Wan

                          #93165
                          Ian S C
                          Participant
                            @iansc

                            If one must use aluminium to build machinery, 7075 T651 tooling plate is the one to try and get (my supplier often has random size off cuts), this stuff machines well, its as tough as steel.

                            Steve, what are the gib strips made of on your machine? Ian S C

                            #93167
                            Steve Wan
                            Participant
                              @stevewan33894

                              Hi Ian

                              Thanks for the interest in my mill machine project. The gibs are brass strip around 3mm thick. Yet to find a way to make taper gibs which is far more harder to master. We don't have much aluminium grade selection in Singapore unless for huge order. I contacted Barry Gordon on his mini-machine making for guidelines. He uses cast iron billets more and aluminium plates for a hollow body while mine is a solid block to add more weight to cut down milling vibrations.

                              You can see the semi raw product of my miller in my photo section.

                              Steve Wan

                              #93172
                              Ian S C
                              Participant
                                @iansc

                                Hi, don"t know if it is practical, but would it be possible to use hollow section aluminium, filled with a epoxy/ concrete mix. Ian S C

                                #93174
                                Steve Wan
                                Participant
                                  @stevewan33894

                                  Hi Ian

                                  Yes! It could be more practical to make a hollow section but I wanted to cut down too many joints for such a small machine. I read a lot about hollow body later filled with concrete/epoxy. Did a discussion here last year.

                                  That will be my next bigger lathe making project in the near future using I beams and stronger AC motor…too early to spell out clearly now.

                                  If you're into similar hobby in mini-machine building, we could be pals and exchange design ideas and suggestions by emails.

                                  Steve Wan

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